Novel Strongly Correlated Europium Superhydrides

We conducted a joint experimental-theoretical investigation of the high-pressure chemistry of europium polyhydrides at pressures of 86-130 GPa. We discovered several novel magnetic Eu superhydrides stabilized by anharmonic effects: cubic EuH , hexagonal EuH , and an unexpected cubic ( 3 ) clathrate phase, Eu H . Monte Carlo simulations indicate that cubic EuH has antiferromagnetic ordering with of up to 24 K, whereas hexagonal EuH and 3 -Eu H possess ferromagnetic ordering with = 137 and 336 K, respectively. The electron-phonon interaction is weak in all studied europium hydrides, and their magnetic ordering excludes -wave superconductivity, except, perhaps, for distorted pseudohexagonal EuH . The equations of state predicted within the DFT+U approach ( were found within linear response theory) are in close agreement with the experimental data. This work shows the great influence of the atomic radius on symmetry-breaking distortions of the crystal structures of superhydrides and on their thermodynamic stability.